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Significant Accounting Policies - Additional Information (Details) ¥ in Thousands, $ in Thousands |  | 12 Months Ended |  |
--- | --- | --- | --- | ---
Jun. 01, 2019 | Dec. 31, 2019 CNY (¥) PerformanceObligation Customer $ / ¥ | Dec. 31, 2018 CNY (¥) | Dec. 31, 2017 CNY (¥) | Dec. 31, 2019 USD ($) Customer $ / ¥ | Jan. 01, 2019 CNY (¥)
Significant Accounting Policies [Line Items] |  |  |  |  |  |
Currency exchange rate, Renminbi ("RMB") to U.S. dollar | $ / ¥ |  | 6.9618 |  |  | 6.9618 |
Rate of VAT | 3.00% | 6.00% |  |  |  |
Advertising expenses |  | ¥ 937,145 | ¥ 983,012 | ¥ 499,294 |  |
Cash and cash equivalents available for conversion to foreign currency |  | ¥ 259,612 | ¥ 157,103 |  |  |
Percentage of cash and cash equivalents available for conversion to foreign currency |  | 18.50% | 12.60% |  | 18.50% |
Right of use asset |  | ¥ 598,991 | ¥ 0 |  | $ 86,040 |
Operating lease liabilities |  | ¥ 656,482 |  |  |  |
Topic 842 |  |  |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |  |  |
Right of use asset |  |  |  |  |  | ¥ 560,200
Operating lease liabilities |  |  |  |  |  | ¥ 607,200
Total Net Revenues | Customer Concentration Risk |  |  |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |  |  |
Number of Customers | Customer |  | 0 |  |  | 0 |
Revenues from customers individually representing portion of total net revenues |  | 10.00% |  |  |  |
Other Income |  |  |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |  |  |
Government subsidies |  | ¥ 14,692 | ¥ 28,688 | ¥ 3,223 |  |
Maximum |  |  |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |  |  |
Time for full refund of transaction price |  | 24 hours |  |  |  |
Time for refund of transaction price to undelivered courses |  | 7 days |  |  |  |
Term of repayment of principal installments on which interest expense and service fees payable |  | 18 months |  |  |  |
Minimum |  |  |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |  |  |
Term of repayment of principal installments on which interest expense and service fees payable |  | 3 months |  |  |  |
Degree- or Diploma-oriented Post-secondary Courses |  |  |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |  |  |
Weighted average service period |  | 32 months |  |  |  |
Professional Certification Preparation and Professional Skills Courses |  |  |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |  |  |
Weighted average service period |  | 19 months |  |  |  |
Online Education Service and Insurance Service [Member] |  |  |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |  |  |
Number of performance obligation | PerformanceObligation |  | 2 |  |  |  |

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